Isothiazolopyrimidine herbicides and method of controlling plant growth

ABSTRACT

A new class of herbicidal compounds consisting of 3,6dialkylisothiazolo(3,4-d)pyrimidin-4(5H)-ones exhibits preemergence and post-emergence herbicidal activity, controlling effectively a wide spectrum of grassy and broad-leafed plant species at rates below one-half pound per acre. The synthesis of members of this class is described in detail, and the utility of representative compounds is exemplified.

United States Patent [191 Gibbons et al.

[4 1 Jan.7, 1975 ISOTHIAZOLOPYRIMIDINE HERBICIDES AND METHOD OFCONTROLLING PLANT GROWTH [75] Inventors: Loren Kenneth Gibbons, Medina;

Arthur Albert Ramsey, Middleport,

both of N.Y.

[73] Assignee: FMC Corporation, New York, NY.

[22] Filed: Aug. 30, 1973 211 Appl. No.: 393,073

Related US. Application Data [62] Division of Ser. No. 189,780, Oct. 15,l97l, Pat. No.

[52] US. Cl. 7l/90 [51] Int. Cl ..A01n 9/12 [58] Field of Search 71/90[56] References Cited UNITED STATES PATENTS 3,080,364 3/1963 Schroederet al 7l/90 3,707,364 l2/l972 Beeke et al. 7l/90 Primary ExamiuerLewisGotts Assistant Examiner Catherine L. Mills [5 7] ABSTRACT 16 Claims, NoDrawings ISOTIIIAZOLOPYRIMIDINE HERBICIDES AND METHOD OF CONTROLLINGPLANT GROWTH This is a division of application Ser. No. 189,780 filedOct. 15, 1971 now issued as U.S. Pat. No. 3,816,420.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionpertains to the general field of herbicides, and particularly tocompositions which control plant growth.

2. Description of the Prior Art Analogous herbicidal compounds aredescribed in copending US. Patent applications Ser. No. 31,414, filedApr. 23, 1970, now US. Pat. No. 3,679,682 and Ser. No. 189,779 and Ser.No. 189,781, filed Oct. 15, 1971.

Neither the isothiazolo[3,4-d]pyrimidin-4-one compounds of the presentinvention, nor the outstanding plant responses in pre-emergence andpost-emergence herbicidal activity of the compounds of the presentinvention, have been previously reported or suggested in the art.

SUMMARY OF THE INVENTION This invention relates to novel herbicidalcompounds, to new herbicidal compositions, and to new methods for thecontrol of undesired plant growth by pre-emergence and post-emergenceapplication of said new and useful herbicidal compositions.

The novel herbicidal compounds of this invention are substitutedisothiazolopyrimidines. The structure of these compounds is given in thefollowing formula:

in which R and R may be the same or different members of the groupconsisting of straight or branched lower aliphatic radicals (l to 4carbon atoms).

Preferred herbicidal isothiazolopyrimidines of this invention are thosecompounds in which both R and R are hydrocarbon radicals. Particularlypreferred are those compounds in which one of R and R is isopropyl ortert-butyl, and the other is a hydrocarbon radical of 1 to 3 carbonatoms or tert-butyl.

Effective herbicidal control of the growth of a wide variety of grassyand broad-leafed plant species is obtained at rates below one-half poundper acre. The herbicidal compositions may be applied and utilized bycommonly accepted methods.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS Thenew class of herbicidal compounds of this invention has the formula:

in which R and R may be the same or different members of the groupconsisting of straight or branched lower aliphatic radicals (l to 4carbon atoms).

The preparation of the new isothiazolopyrimidines of this invention maybe conveniently carried out from readily available materials. Methods ofsynthesis are illustrated by the following schema, wherein a herbicidalisothiazolopyrimidine of the invention is designated V, and R and R havethe significance set forth above.

While methods for preparing intermediates used in the synthesis of theisothiazolopyrimidines of this invention have previously been described,in order that the new compounds of this invention may be readilyavailable to those skilled in the art, the methods for the preparationof those intermediates used in the examples are summarized brieflybelow. The examples describing the synthesis of theisothiazolopyrimidines follow the description of the preparation of theintermediates. All temperatures are in degrees centigrade. All reducedpressures not otherwise specified are the reduced pressure normallyattainable with a water aspirator.

The intermediate methyl dithioalkanoates (l of the schema) were preparedby the reaction of methyl mercaptan and hydrogen chloride with theappropriate alkanenitrile, followed by thiohydrolysis in pyridine withhydrogen sulfide. This procedure has been described by Mayer,Scheithauer & Kunz, Chem. Ber. 99,1393 (1966). The following compoundswere prepared:

methyl dithioacetate, b.p. 5051/30mm Hg;

methyl dithiopropionate, b.p. /40mm Hg;

methyl dithiobutyrate, b.p. 76l29mm Hg;

methyl dithioisobutyrate, b.p. 485 ll8mm Hg;

methyl dithiotrimethylacetate, b.p. 65-67/12mm Hg.

An alternate to the method of Mayer et al for preparation ofdithioesters (I) is the method of Peak and Stansfield, J. Chem. Soc.,4067 (1966), employing the Willgerodt-Kindler reaction to form athioalkylmorpholide, followed by methylation and then thiohydrolsis.

Dithioesters (I) react with malononitrile to form the sodium salt of thedesired 2-cyano-3-mercapto-2- alkenenitrile (II of the schema) by themethod of Hartke and Peshkar, Archiv. Pharm. 301, 601 (1968).

Sodium salts of the following compounds were prepared:

2-cyano-3-mercapto-2-butenenitrile; 2-cyano-3-mercapto-2-pentenenitrile;2-cyano-3-mercapto-4-methyl-Z-pentenenitrile;2-cyano-3-mercapto-4,4-dimethyl-2-pentenenitrile; and2-cyano-3-mercapto-2-hexenenitrile. The sodium salts are used in thenext step without rigorous purification.

The sodium salt (11) is converted to 3-amino-4- cyano-S-alkylisothiazole(III of the schema) by a method similar to that of Hartke and Peshkar,Archiv. Pharm. 301, 611 (1968), involving reaction with monochloramine,formed from ammonium hydroxide and sodium hypochlorite. The followingcompounds were prepared and their structures were verified by infraredand nmr spectral analysis:

3-amino-4-cyano-5-methylisothiazole, m.p. l76.5177.5;

3-amino-4-cyano-5-ethylisothiazole, m.p. l53.5l55;

3-amino-4-cyano-5-isopropylisothiazole, m.p. 838 5;

3-amino-5-tert-butyl-4-cyanoisothiazole, m.p. 455

3-amino-4-cyano-5-pr0pylisothiazole, m.p.

l23.5-l24.5. Intermediate 3-amino-5-alkylisothiazole-4- carboxamides (IVof the schema) were prepared by hydrolyzing the appropriate3-amino,-4-cyano-5- alkylisothiazoles with concentrated sulfuric acid.The following compounds were prepared and their structures were verifiedby infrared or nmr spectral analysis:

3-amino-5-isopropylisothiazole-4-carboxamide,

3-amino-5-tert-butylisothiazole-4-carboxamide,

m.p. ll8-120.

The methods used for the preparation of the iso thiazolopyrimidines ofthe invention (V in the schema) are described in the following examples:

EXAMPLE I 6-Ethyl-3-isopropylisothiazolo[3,4-d]pyrimidin- 4(5H)-one Oneml of concentrated sulfuric acid was added dropwise to a suspension of 2g of 3-amino-4-cyano-5- isopropylisothiazole in 4 ml of propionicanhydride at 0. The reaction mixture was heated for one hour on a steambath and poured onto crushed ice. The suspension was filtered and thefiltrate was made basic with dilute ammonium hydroxide to yield 2.1 g ofproduct; m.p. l60161. An additional 0.9 g sample of product (m.p.162.5163.5) was prepared in a similar manner. The solids were combinedand recrystallized twice from ethyl acetate-hexane to give purified6-ethyl-3- isopropylisothiazolo[ 3,4-d ]pyrimidin-4(5H )-one; m.p.

Analysis: Calc'd for C H N OS: C 53.80; H 5.87; N 18.83 Found: C 53.39;H 5.68; N 18.71

EXAMPLE II 3-Isopropyl-6-propylisothiazolo[3,4-d1pyrimidin- 4(5I-l)-oneBy the method of Example I, 3.6 ml of concentrated sulfuric acid wasslowly added to a mixture of 5.9 g of3-amino-4-cyano-5-isopropylisothiazole in 25 ml of butyric anhydride,maintaining the temperature at 5-20 throughout the addition. The mixturewas treated as in Example I to obtain a white solid. This solid wasdissolved in 20 ml of glacial acetic acid and the solution heated at 50for 1 hour. The hot solution was filtered and poured into 200 ml ofwater and the slurry thus obtained was cooled in an ice'bath. The solidwas collected and recrystallized from ethanol-water to give 1.8 g of3-isopropyl-6- propylisothiazolo[3,4-d]pyrimidin-4(5H)-one, m.p.102-104. The ir and nmr spectra of the product were consistent with theassigned structure.

Analysis: Calcd for C H N oSz C 55.67; H 6.37;

N 17 Found: C 55.68; H 6.20; N l

EXAMPLE Ill Analysis: Calcd for C,,H N;,OS: C 5 Found: C 5

EXAMPLE IV 6-tert-Butyl-3-isopropylisothiazolo[3,4-d]pyrimidin-4(5H)-one To a mixture of 10 g of 3-amino-4-cyano 5-isopropylisothiazole and 15.6 g of trimethylacetyl chloride was slowlyadded 7 ml of concentrated sulfuric acid. The temperature of thereaction mixture slowly increased to during the addition. The mixturewas heated at for 2 hours and the hot mixture was poured into ice-water.The mixture was neutralized to pH 7.5 by addition of sodium bicarbonate.The solid was isolated and dried to give 8.9 g of crude6-tertbutyl-3-isopropylisothiazolo-[3,4-d]pyrimidin- 4(5I-I)-one, m.p.202204. Recrystallization from methanol-water increased the meltingpoint to 202.5203.5. The ir and nmr spectra were consistent with theassigned structure.

Analysis: Calc'd for C H N OS: C 57.11; H 7.18; N 16.65 Found: C 56.85;H 6.93; N 16.76

EXAMPLE V 3-Isopropyl-6-methylisothiazolo[3,4-dlpyrimidin- 4(5H)-one Bythe procedure of Example I, a suspension of 10 g of3-amino-4-cyano-5-isopropylisothiazole in 13.3 g of acetic anhydride wastreated dropwise with 7 ml of concentrated sulfuric acid at 5. Thesuspension was heated on a steam bath for one hour, poured over ice andextracted with ethyl acetate. The ethyl acetate extracts wereconcentrated under reduced pressure to give solid product. This productwas recrystallized several times from ethyl acetate at -80 to give 9.0 gof 3- isopropyl-6-methylisothiazolo[3,4-d]pyrimidin- 4(5I-I)-one; m.p.204206. The ir and nmr spectra of the product were consistent with theassigned structure.

Analysis: Calcd for C H,,N OS: C 51.67; H 5.30; N 20.09 Found: C 51.51;H 5.07; N 19.87

EXAMPLE VI 3-Ethyl-6-isopropylisothiazolo[3,4-d1pyrimidin- 4(5H)-one Bythe method of Example I, a mixture of 7 g of 3-amino-4-cyano-5-ethylisothiazole and 15.8 g of isobutyric anhydride wastreated with 5 ml of concentrated sulfuric acid and the mixture heatedon a steam-bath for 1.75 hours, then poured into ice-water. The aqueousmixture was extracted thrice with ethyl acetate, the extracts combinedand concentrated by evaporation under reduced pressure to give an oilwhich crystallized at dry ice temperature. The solid was recrystallizedfrom cyclohexanehexane to give 3.1 g of 3-ethyl-6-isopropylisothiazolo[3,4-d]pyrimidin-4(51-l)-one, m.p. 150-151. The irand nmr spectra were consistent with the assigned structure.

Analysis: Calcd for C H N OS: C 53.80; Found: C 53.65.

EXAMPLE VII 6-tert-Butyl-3-ethylisothiazolo[ 3,4-d1pyrimidin-4(5l-l)-one By the method of Example W, 15.6 g of trimethylaceticanhydride and g of 3-amino-4-cyano-5- ethylisothiazole were reacted inthe presence of 7 ml of concentrated sulfuric acid to give 15.7 g of6-tert-butyl- 3-ethylisothiazolo[3,4-d]pyrimidin-4(5H)-one; m.p.198.5-l99.5 on recrystallization from methanolwater. The ir and nmrspectra were consistent with the assigned structure.

Analysis: Calcd for C H N OS: C 55.68; H 6.37; N 17.71 Found: C 55.78; H6.31; N 17.47

EXAMPLE VIII Analysis: Calcd for C H N OS: C 57.35; H Found: C 57.35; H

EXAMPLE IX 3-tert-Butyl-o-ethylisothiazolo[3,4-d]pyrimidin- 4(5H)-oneThree hundred ml of concentrated sulfuric acid was slowly added to 37.5g of 3-amino-5-tert-butyl-4- cyano-isothiazole while maintaining thetemperature below The mixture was then heated at for 3.5 hours. The hotmixture was poured into ice-water and the solution neutralized (to pH 9)by addition of concentrated ammonium hydroxide. The solution wasextracted thrice with ethyl acetate and the combined extracts evaporatedto dryness to give 36.6 g of solid which by recrystallization fromtoluene gave 18.7 g of 3-amino-5-tert-butylisothiazole-4-carboxamide,m.p. l42l43. The ir and nmr spectra were consistent with the assignedstructure.

6.5 Found: C 48.21; H 6.8

A mixture of 5 g of 3-amino-5-tert-butylisothiazole- 4-carboxamide and10 ml of propionic anhydride was cooled to 0 and to it was slowly added,while maintaining the temperature below 0, 2 ml of concentrated sulfuricacid. The mixture was then heated for 2.5 hours on a steam-bath and thehot mixture poured into icewater. The white solid was isolated and theaqueous filtrate extracted thrice with ethyl acetate. The combinedextracts were concentrated by evaporation to dryness under reducedpressure. The residue and previously isolated solid were combined andrecrystallized from methanol-water to give 5.4 g of3-tert-butyl-6-ethyl-isothiazolo[3,4-d]pyrimidin-4(5H)-one, m.p.l79-l80. This product was identical with the product obtained byreaction of propionic anhydride and3-amino-5-tertbutyl-4-cyanoisothiazole according to the method ofExample I.

The ir and nmr spectra of the product were consistent with the assignedstructure:

Analysis: Calc'd for c,,ii,,N.os= C 55.68; H 6.37; N l7.7l Found: C55.94; H 6.30; N 17.86

The following additional compounds of the invention were prepared bymethods exemplified above: Example X.

3 -tert-Butyl-6-methylisothiazolo[ 3 ,4-d pyrimidin- 4(5I-I)-one, m.p.206-207. Example XI.

6-Ethyl-3-propylisothiazolo[3,4-d]pyrimidin- 4(5I-I)-one, m.p.132.5-l33.5. Example XII.

6-Isopropyl-3-methylisothiazolo[3,4-d]pyrimidin- 4(5I-I)-one, m.p.l82.5-l84.5 Example XIII.

6-Ethyl-3-methylisothiazolo[ 3 ,4-d]pyrimidin- 4(5I-I)-one, m.p.245-246. Example XIV.

3,6-Diethylisothiazolo[3,4-d]pyrimidin-4(5I-I)-one,

m.p. I58159. Example XV.

6-MethyI-3-propylisothiazolo[3,4-dlpyrimidin- 4(5I'I)-one, m.p. I83-184.Example XVI.

3-Ethyl-6-methylisothiazolo[3,4-d]pyrimidin- 4(5I-I)-one, m.p. 249250.Example XVII.

6-Isopropyl-3-propylisothiazolo[3,4-d]pyrimidin- 4(5l-I)-one, m.p.l54-I55. Example XVIII.

6-tert-Butyl-3-methylisothiazolo[3,4-d1pyrimidin- 4(5I-I)-one, m.p.236237.5. Example XIX.

3-tert-Butyl-6-isopropylisothiazolo[3,4-d]pyrimidin- 4(5I-I)-one, m.p.220223. Example XX.

3,6-Di-tert-butylisothiazolo[3,4-d1pyrimidin- 4(5I-I)-one, m.p. 287-289.

The biological activity of the compounds of this invention wasdemonstrated in standard herbicidal tests. The test methods and testresults were as follows:

For pre-emergence herbicidal tests, seeds of lima beans(Phaseolus'lunatus), corn (Zea mays), lettuce (Lactuca saliva), mustard(Brassica juncea), and crabgrass (Digitaria sanguinalis) were planted inshallow flat-bed trays containing two to three inches of loam soil.Within twenty-four hours after planting an aqueous-acetone solution ofthe compound being testedwas sprayed on the soil at a rate of 8 poundsactive ingredient per acre. Test plants were maintained in a greenhouseand watered regularly for two weeks, after which time the phytotoxicityof the compound was recorded. Individual plant species were examined forper cent kill and vigor. Untreated control plants were maintained inevery test carried out.

Table l lists results of pre-emergence herbicidal testmg:

Table l I Ere-emergence Evaluation of Compounds at 8 lb/acre CompoundTest Plant Species of Lima Corn Lettuce Mustard Crab- Example Beansgrass l 0* 0 0* 100 30 II 100 70* I00 I00 I00 III I00 I00 I00 I00 95* IVI00 I00 I00 I00 I00 V I00 70* I00 I00 90* VI 90* I00 I00 100 I00 VII 7I00 I 100 I00 I00 90* VIII I00 100 I00 I00 I00 IX I00 0* 90* I00 90* X100 0 I00 I00 I00 XI I00 70* I00 I00 100 XII 'I00 70* I00 I00 I00 XIIII00 70 I00 I00 I00 XIV I00 70* 95* I00 I00 XV 25 0 I00 I00 I00 XVI 90*0* 95* I00 I00 XVII I00 100 I00 I00 I00 XVIII I00 100 I00 I00 I00 XIX90* 0* 90* I00 I00 XX I00 0 70* I00 I00 *Plants not dead were severelydamaged and not expected to live.

For post-emergence herbicidal tests the test crop seeds were planted inshallow flat-bed trays containing two to three inches of a loam soil.The growth trays were maintained in a greenhouse and regularly wateredfor approximately two weeks. When the first trifoliate leaves of beanplants were unfolding, the test plants were removed from the greenhouseand sprayed with a aqueous-acetone solution of the compound being testedat a rate of 8 pounds active ingredient per acre. The plants weremaintained in the greenhouse and watered regularly for an additional twoweeks, after which time the phytotoxicity of the compound was recorded.

Individual plant species were examined for per cent kill LII and vigor.Untreated control plants were maintained in every test carried out;

Table II lists the results of post-emergence herbicidal testing:

'Table II Post-emergence Evaluation of Compounds at 8 [acre CompoundTest Plant Species of Lima Corn Lettuce Mustard Crab- Example Beans Igrass l I00 I00 I00 I00 100 II 0 0 0 20 0 III I00 I00 I00 I00 I00 IV 100I00 I00 I00 I00 V 100 I00 I00 I00 100 VI I00 I00 I00 I00 I00 VII I00 I00I00 I00 I00 VIII I00 I00 I00 I00 I00 IX I00 I00 I00 100 X I00 30* I00I00 I00 XI I00 I00 I00 I00 I00 XII I00 I00 I00 I00 I00 XIII 100 70" I00I00 I00 XIV I00 50 I00 I00 I00 XV I00 30" I00 100 I00 XVI I00 I00 I00I00 XVII I00 I00 I00 I00 I00 XVIII I00 I00 I00 I00 I00 XIX I00 30 I00I00 I00 XX 30* 0 0 0 0 Plants not dead were severely damaged and notexpected to live.

For herbicidal applications, the isothiazolopyrimidines of thisinvention may be utilized in diverse formulations, including theagricultural adjuvants and agricultural carriers, i.e., those materialsnormally employed to facilitate the dispersion of active ingredients inagricultural applications, recognizing the fact that the formulation andmode of application of a toxicant may affect the activity of thematerial in a given application. Thus, a compound of this invention maybe formulated as a granule of relatively large particle size, as awettable powder, as a emulsifiable concentrate, as a solution, or as anyof several other known types of formulations, depending on the desiredmode of application.

Granular formulations are particularly useful for ae rial distributionor for penetration of a canopy of foliage. Useful granular formulationsmay be of several types. lmpregnated granules are those wherein theactive ingredient is applied to large particles of an absorbent carrier,such as an attapulgite or kaolin clay, corncobs, expanded mica, etc.,normally in the form of a solution in a solvent. Surface-coated granulesmay be produced by spraying the molten active ingredient onto thesurface of a generally nonabsorbent particle or by spraying on asolution of active ingredient in a solvent. The core may bewater-soluble such as a prilled fertilizer, or insoluble such as sand,marble chips or coarse talc. Particularly useful is a granule wherein awettable powder is applied as a surface coating to a sand or otherinsoluble particle such that the wettable powder may be dispersed oncontact of the granule with moisture. Granules may may be produced byagglomeration of dusts or powders by compaction rollers, by extrusionthrough a die or by use of a granulating disc. Granular formulations mayvary widely in concentration, with useful formulations containing aslittle as 0.5 percent or as much as 95 percent of active ingredient.

Wettable powders, also useful formulations for both preandpost-emergence herbicides, are in the form of finely divided particleswhich disperse readily in water or other dispersants. The wettablepowder is ultimately applied to the soil either as a dry dust or as anemulsion in water or other liquid. Typical carriers for wettable powdersinclude fullers earth, kaolin clays, silicas and other highly absorbent,readily wet inorganic diluents. Wettable powders normally are preparedto contain about percent to 80 percent of active ingredient, dependingon the absorbency of the carrier, and usually also contain a smallamount of a wetting, dispersing or emulsifying agent to facilitatedispersion. For example, a useful wettable powder formulation contains80.8 parts of an isothiazolopyrimidine of this invention, 17.9 parts ofpalmetto clay, and 1.0 part of sodium lignosulfonate and 0.3 part ofsulfonated aliphatic polyester as wetting agents.

Other useful formulations for herbicidal applications are theemulsifiable concentrates, which are homogeneous liquid or pastecompositions dispersible in water or other dispersant, and may consistentirely of the compound of this invention with a liquid or solidemulsifying agent, or may also contain an agriculturally acceptableliquid carrier, such as xylene, heavy aromatic naphthas, isophorone andother nonvolatile organic solvents.

Typical wetting, dispersing or emulsifying agents used in agriculturalformulations include, for example, the alkyl and alkylaryl sulfonatesand sulfates and their sodium salts; polyethylene oxides; sulfonatedoils, fatty acid esters of polyhydric alcohols; and other types ofsurface-active agents, many of which are available in commerce. Thesurfaceactive agent, when used, normally comprises from 1 percent to 15percent weight of the herbicidal composition.

These formulations may be applied without further dilution or as dilutesolutions, emulsions or suspensions in water or other suitable diluent.The compositions may be applied to the area wherein control is desiredby spraying onto the undesired vegetation or onto the surface of thesoil in the case of liquid compositions or by distribution frommechanical equipment in the case of solids. The surface-applied materialmay also be blended into the upper layer of soil by cultivation, or leftas applied, as is appropriate to gain the optimum results with theparticular treatment.

The active herbicidal compounds of this invention may be formulatedand/or applied with insecticides, fungicides, nematocides, plant-growthregulators, fertilizers, and other agricultural chemicals. In applyingan active compound of this invention, whether formulated alone or withother agricultural chemicals, an effective amount and concentration ofan isothiazolopyrimidine are of course employed.

It is apparent that various modifications may be made in the formulationand application of the novel compounds of this invention, withoutdeparting from the inventive concept herein, as defined in the followingclaims.

We claim;

1. An herbicidal composition containing, as active ingredient, aneffective amount of a compound of the formula:

RI A wherein R and R are members of the group consisting of straight andbranched alkyl radicals of l to 4 carbon atoms, in admixture with anagricultural carrier.

2. An herbicidal composition of claim 1 in which R is a member of thegroup consisting of methyl, ethyl propyl, isopropyl and tert-butylradicals; and R is a member of the group consisting of isopropyl andtertbutyl radicals.

3. An herbicidal composition of claim 1 in which R is a member of thegroup consisting of isopropyl and tert-butyl radicals and R is a memberof the group consisting of methyl, ethyl, propyl, isopropyl andtert-butyl radicals.

4. An herbicidal composition of claim 1 in which the compound is3,6-diisopropylisothiazolol3,4- d]pyrimidin-4(5H)-one.

5. An herbicidal composition of claim 1 in which the compound is6-tert-butyl-3-isopropylisothiazolo[3,4- d]pyrimidin-4(5H)-one.

6. An herbicidal composition of claim 1 in which the compound is6-tert-butyl-3-propylisothiazolo[3,4- d]pyrimidin-4(5H)-one.

7. An herbicidal composition of claim 1 in which the compound is6tert-butyl-3 ethylisothiazolo[3,4- d]pyrimidin4(5I-l)-one.

8. An herbicidal composition of claim 1 in which the compound is6-ethyl-3-isopropylisothiazolo[3,4- d]pyrimidin-4(5H)-one.

9. A method of controlling undesired plant growth which comprisesapplying to the locus where control is desired an effective amount of acompound of the formula:

wherein R and R are members of the group consisting of straight andbranched alkyl radicals of l to 4 carbon atoms.

10. A method according to claim 9 in which R is a member of the groupconsisting of methyl, ethyl, propyl, isopropyl and tert-butyl radicals;and R is a member of the group consisting of isopropyl and tert-butylradicals.

11. A method according to claim 9 in which R is a member of the groupconsisting of isopropyl and tertbutyl radicals and R' is a member of thegroup consist- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 5,859,074 DATED January 7 975 INVENTOR(S) L.K.Gibbons andA.A.Ramsey It is certified that error appears in the'above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, formula at lines 60-65, "R" at 6-position should be Column 5,line 46, insert hyphen between "cyolohexane" and v "hexane".

Column 5, line 66, insert hyphen between "methanol" and "water".

c l mn 10, line 2, after "5L5 percent", insert Y---- Signed and Sealedthis second Day of Decemberlflj [SEAL] Attest:

. RUTI c. MASON c. lulsluu. DANN A nesting Offirer Commissioner ufPar'nn and Trademarks

1. AN HERBICIDAL COMPOSITION CONTAINING, AS ACTIVE INGREDIENT, ANEFFECTIVE AMOUNT OF A COMPOUND OF THE FORMULA:
 2. An herbicidalcomposition of claim 1 in which R is a member of the group consisting ofmethyl, ethyl propyl, isopropyl and tert-butyl radicals; and R'' is amember of the group consisting of isopropyl and tert-butyl radicals. 3.An herbicidal composition of claim 1 in which R is a member of the groupconsisting of isopropyl and tert-butyl radicals and R'' is a member ofthe group consisting of methyl, ethyl, propyl, isopropyl and tert-butylradicals.
 4. An herbicidal composition of claim 1 in which the compoundis 3,6-diisopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 5. Anherbicidal composition of claim 1 in which the compound is6-tert-butyl-3-isopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 6. Anherbicidal composition of claim 1 in which the compound is6-tert-butyl-3-propylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 7. Anherbicidal composition of claim 1 in which the compound is6-tert-butyl-3-ethylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 8. Anherbicidal composition of claim 1 in which the compound is6-ethyl-3-isopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 9. A method ofcontrolling undesired plant growth which comprises applying to the locuswhere control is desired an effective amount of a compound of theformula:
 10. A method according to claim 9 in which R is a member of thegroup consisting of methyl, ethyl, propyl, isopropyl and tert-butylradicals; and R'' is a member of the group consisting of isopropyl andtert-butyl radicals.
 11. A method according to claim 9 in which R is amember of the group consisting of isopropyl and tert-butyl radicals andR'' is a member of the group consisting of methyl, ethyl, propyl,isopropyl and tert-butyl radicals.
 12. A method according to claim 9 inwhich the compound is3,6-diisopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 13. A methodaccording to claim 9 in which the compound is6-tert-butyl-3-isopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 14. Amethod according to claim 9 in which the compound is6-tert-butyl-3-propylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 15. A methodaccording to claim 9 in which the compound is6-tert-butyl-3-ethylisothiazolo(3,4-d)pyrimidin-4(5H)-one.
 16. A methodaccording to claim 9 in which the compound is6-ethyl-3-isopropylisothiazolo(3,4-d)pyrimidin-4(5H)-one.